Zinc aluminum anode for electrodeposition of zinc



Patented Nov. '15, 1932 UNITED STATES PATENT OFFICE ARTHUR K. GRAHAM, 0F SEAGIRTyNEW JERSEY, ASSIGNOR 'l'u HANSON-VAN WINKLE- IUNNING COMPANY, OF MATAWAN, NEW JERSEY, A CORPORATION OF NEW JERSEY.

ZINC ALUMINUM ANODE FOB ELECTRODEPOSITION OF ZINC 10 Drawing.

the, metal in the form .of soluble salts of the metal, and furthermore tends to maintain the metal content and acidity of the bath more uniform;

In the electrodeposition of zinc fromiacld baths, for example, the use of pure zinc anodes, which are soluble in the bath, has led to certain difliculties due. partly to the fact that such an anode is chemically soluble in the bath even when no external voltage is applied, with the result that a serious loss of metal occurs during idle periods, and even during the electroplating operation the corrosion or solution ofthe anodeoccurs at a greater rate than the deposition of the metal upon the cathode. Consequently, the metal content of the bath increases and the acidity of the bath-diminishes. The indicated anode efiiciency of pure zinc'anodes may in a. given case be in the neighborhood of 107%, and

suspended particles of metal or sludge .freed from the anode find their way to the cathode where theyadhere as inclusions to the detriment of the electrodeposit both with respect to its appearance and with respect to its protective quality on the article being plated. The indicated cathode efliciency due to such higher than 100%. I

Many of the disadvantages of pure zinc anodes in acid baths are also present to some extent in the use of such anodes in cyanide baths.

My invention has for its-object to provide an improved soluble anode for use in the electrodeposition of zinc, from either acid or cyanide baths.

In accordance with my invention the anode comprises zinc with a small addition of aluminum. The zinc and aluminum a'reprefer- Application filed February 20, 1931. Serial No. 517,307.

ably fused together as an alloy or. intimate homogeneous mixture, and then cast in molds or otherwise formed. The proportion of aluminum to zinc may Vary from, for example, .25 '0 to about 5%01? aluminum, but I usually employ between 25% and 1% aluminum.

The addition of small quantities of aluminum to zinc confers upon the anode important chemica-land electrochemical properties. It reduces the rate of chemical solution ofthe anode, reduces the indicated anode efliciency, reduces the formation of sludge, improves the grain structure of the anode, causes the anode to corrode more evenly, brings about an approximate equalizatlon of anode and cathode elhciencies without the occurrence of objectionable inclusions of sludge and suspended matter in the electrodeposit, and maintains the metal content and acidity of the solution much more uniform than in the use of pure zinc anodes. The electrodeposit, when using zinc" anodes containing aluminum, is of better appearance and textureand offers better protective properties on the electroplated article;

Comparative tests of anodes composed of zinc with additions of aluminum, and anodes composed of substantially pure-zinc, showed in the case of acid baths, for example, an anode efficiency of 106.9% with the addition of 27% aluminum to the zinc, an anode efli: ciency of 104.7% with an addition of 37% aluminum to the zinc, and anv anode etficiency of 101.5%. with an addition of 174% alumi 1111111 to the zinc, whereasfour samples of pure zinc showed anode efficiencies ranging from 106% to 107.6%. Anaddition 015.27% alu inclusions is also frequently found .to be m'inum .to pure zinc lowered the cathode etfihanging idle in the solution than an anode of pure zinc. The metal content of the solution'showed after forty-eight hours run a large increase when usingpure zinc anodes,

and a very slight decreas'e'with small addi tions of aluminum to the zinc anode.. In the same timethe acidity of the-bath showed substantial decrease when using pure zinc 1 a i i 1,aas,2og

anodes and negligible decrease, or even a slight increase, w en using anodes of zinc with small additions of aluminum. The ain structure on corrosion showed much- 5 nor in the case of the zinc anodes containing small additions of aluminum than in anodes of pure zinc. The sludge formation was also greatly reduced'in the case of anodes contalning small additions of aluminum. Each test was conducted with the anode and cathode areas equal.

From the above observations it will be seen that the various factors are subject to control by varying the proportion of aluminum to mm in the anode, and that the most desirable conditions are obtained with the addition of from say, to .75% aluminum to pure 21110.

I claim go 1. Arzinc anode having a small content of aluminum amounting to less than 5%;

.2. A zinc anode containing from 25% to 1% aluminum.

3. A zinc anode containing from -.25%

- 26 to .75% aluminum.

ARTHUR K. GRAHAM. 

